Ammonium nitrate slurry blasting
composition containing sulfur-
sodium nitrate sensitizer

ABSTRACT

THIS INVENTION IS AN IMPROVED BLASTING AGENT COMPOSITION OF AMMONIUM NITRATE IN A PREDOMINANTLY AQUEOUS SLURRY WITH A SENSITIZER WHICH IS A COMBINATION OF ELEMENTAL SULFUR AND SODIUM NITRATE. THE SENSITIZER IS FREE OF SELF EXPLOSIVE INGREDIENTS PROVIDING GREATER SAFETY IN HANDLING AND PROCESSING OF THE EXPLOSIVE COMPOSITION.

United States Patent Ofice Re. 27,095 Reissued Mar. 23, 1971 27,095MIMONIUM NITRATE SLURRY BLASTING CODIPOSITION CONTAINING SULFUR- SODIUMNITRATE SENSITlZm RobctLClny,llonnflhl,a-d1exLUdy,SaltLake C8,. U, mResearch and Original No. 3,249,411, m Ma 3, 1966, so. No. 364,289 May 11964. A tin reissue Jan. 14,1910, so. No. 1,550

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ABSTRACT or run DISCLOSURE This invention is an improved blasting agentcomposition of ammonium nitrate in a predominantly aqueous slurry with asensitizer which is a combination of elemental sulfur and sodiumnitrate. This sensitizer is free of self explosive ingredients providinggreater safety in handling and processing of the explosive composition.

The present invention relates to an improved blasting agent composition.It has particular application to low cost-explosives which are waterplasticized or liquefied, i.e., those containing substantial propertiesof ammonium nitrate combined with suitable fuels and with enough liquid(usually water) to form a fluid slurry or aplastic and at least somewhatflowable mass that can be poured into boreholes, etc. The invention alsocontemplates use of other appropriate additive materials, includingsensitizers, fuels, etc. which preferably are normally nonexplosive bythemselves.

In recent years increasing quantities of explosives that are plastic, orliquid in nature, have gone into use for mining and blasting operations.They offer considerable cost savings, as compared with many otherblasting agents. Most of these have involved use of substantialquantities of inorganic nitrates, preferably ammonium nitrate orammonium nitrate 'with sodium nitrate, modified, e.g. by adding asuitable fuel or other material. The inorganic nitrate, which is usuallythe largest component, generally is not sutficiently sensitive per sefor mining and blasting operation. Moreover, it is primarily an oxidizerand requires addition of fuel or a reducer for good chemical balance.Various compositions have been made up to improve the performance of thebasic inorganic nitrate ingredient. In some cases, it has previouslybeen suggested, sodium nitrate may be used to replace partof theammonium nitrate. Various other additives, including nitrated organicmaterials such as cellulose nitrate (smokeless powder) trinitrotoluene(TNT), nitromethane and the like, reducing metals such as powderedaluminum, and fuels such as sulfur, carbonaceous materials,hydrocarbons, etc., have been added. In some respects the most effectiveand satisfactory sensitizers have been the explosive or nitrated organicadditives such as TNT, picric acid, nitro-starch, smokeless powder andthe like. These materials contribute energy as well as improving thesensitivity of ammonium nitrate. However, these explosive materialsalways involve certain hazards in handling and processing.

Some of the materials named above as sensitizers are commonly employedin finely divided form and they often tend to accumulate in pockets,hidden recesses and the like, for example in processing equipment, thuscreating potentially dangerous sites and situations. An important ob ect of the present invention is to create a blasting agent. particularlya slurry blasting agent, of suitable sensitivity and adequate energywhich does not require the use of the explosive sensitizers named above.The primary obect of this aspect of the invention is, of course, toachieve greater safety. This is accomplished while still using the ma orcomponents mentioned above, including specifically ammonium nitrate andsodium nitrate. a

For large scale blasting operations, e.g. for blasting iron ore inquantity, the blasting agent must be sensitive enough for thoroughdetonation at the borehole temperature, in columns of conventionaldiameter (usually around 6 to 9 inches, although smaller and largerdiameter bores are used) and in lengths several times their diameter.Borehole temperatures may vary from about 0' C. to 30 C., depending upongeographical location, primarily. At

the same time, the blasting agent should not be so sensitive as toinvolve any substantial risk of explosion during-normal shipping,handling, or while putting it in the borehole for use. These variousoperations are now being carried out more and more by mechanical means,e.g., by slurry mixing and pumping machinery or by mixing and packagingequipment. Obviously, the slurry composition must not be sensitiveenough to explode in small masses when subjected to moderate friction orshock of the character inherent in operation of such machinery. As ageneral working rule, the slurry, when finished and ready fordetonation, should have a sensitivity suitable for its selfpropagationof explosion in a continuous column, e.g. six diameters in length ormore and not more than 9 orl O inches in diameter, unconfined, at theborehole temperature. For far northern areas, or shallow operations inwinter time, the explosive must be detonable at temperatures as low as 5C. In other cases, the explosive need be detonable only at temperaturesas high as 35' C. Sensitivity must not be too great, however, and acritical diameter of about 1% to 2 inches is usually the lower workinglimit, at working temperatures. A 6-inch diamete column gives goodgeneral test results. A specific object of the present invention is toprepare a slurrytype blasting agent, based primarily on ammoni umnitrate, but also containing sodium nitrate, which will meet the abovesensitivity tests both minimum and maximum and still not necessarilycontain any of the more hazardous sensitizers such as the nitratedorganic materials which are normally explosive per se. i; An importantaspect of this invention is the discovery that by using well chosenproportions of sulflm'falong with sodium nitrate, the sensitivity ofhigh nitrate explosives, particularly those containing water, may becontrolled very satisfactorily. By high ammonium nitrate it is intendedto mean those compositions which contain 40% by weight or more,preferably at least of ammonium nitrate. The sulfur is preferablyrelated to the sodium nitrate, in proportion, preferably being between10 and 30% of the weight of sodium nitrate, PI'OPOF tions of about 1 to5 being especially preferred.

In order to give flexibility for use'under various conditions, it isoften desirable to be able to control or to vary the sensitivity of thecomposition over reasonably wide ranges by adding varying but generallyrelatively small amounts of one or more potent sensitizer which is notexplosive per se. It is also desirable that such a sensitizer have alsothe further property of adding energy to the composition, preferably asa fuel or reducing agent since oxidizer is commonly in excess in highammonium nitrate explosive. It is of course desirable that all theingredients contribute energy to the explosion, as far as it is possibleto find economical ingredients having the retired properties. However,other properties such as lidity, sensitivity, compatibility with eachother, etc. are so important. Aluminum powder of appropriate par- :lesize and surface characteristics is very suitable in impositions of thistype as an aid in controlling sensivity. By adding a small amount ofsuch material, the :mperature at which the explosive will meet therequired :nsitivity tests named above, e.g., the 6-inch unconfined olumnself-propagating test, etc., may be substantially reuced. 'Finelydivided aluminum also adds appreciably the explosive energy. Thus theinvention contemplates so of aluminum as a supplemental sensitizer andenerizer.

Since both ammonium nitrate and sodium nitrate are Ixidiurs, thesecompositions often need a fuel or reducing gent for bringing thecomposition into better chemical P8181160. It is often desirable,therefore, to add fuels in tddition to or in lieu of such aluminum, e.g.Carbohydrates 'uch as starch, or sugar, or carbonaceous fuels such as001, asphalt, charcoal, gilsonite. These are additional to he sulfur. Itis often desirable in liquid or slurry composiions, to use liquids whichassist in the slurrying or liquefyng of the composition and alsocontribute fuel energy. To ncrease the energy of blasting compositionscontaining aoth sodium nitrate and sulfur, by adding energy from variousfuel sources, including those just named, and without detracting fromother essential properties is still mother object of this invention.

It is desirable also that the explosive composition have as high adensity as possible, consistent with other necestary qualities orproperties. Obviously, increased density permits the use of a greaterweight of blasting agent in a borehole of given dimensions. However,increasing the density of a given composition normally also tends todecrease sensitivity, particularly in slurry-type or water plasticizedblasting agents. Hence a further object of this invention is to make ablasting composition of optimum or near optimum density which has alsothe properties of optimum or near optimum sensitivity, together withadequate power, appropriate brisance, etc.

The nature of the present invention, and of the foregoing objects, andof others which are inherent or which will appear below, will be morefully understood and appreciated after a detailed description of theprinciples of the invention and specific examples of its preferred formsare explained.

A preferred general composition, according to the present invention,comprises a thick aqueous slurry containing a larger proportion ofammonium nitrate in solution and including at least a small amount ofsodium nitrate. From about 40 to 70% by weight of ammonium nitrate isused. The preferred range of ammonium nitrate is about 50 to 60%. Watercontent, or rather liquid content, since some of the water may bereplaced with a compatible liquid fuel such as ethylene glycol,glycerine, or other lower aliphatic alcohols, should be between about 10and by weight of the total composition. Preferably the liquid is usuallybetween 12 and 16%.

Proportions totaling from about 5 to by weight of sodium nitrate arepreferably included in addition to the ammonium nitrate. It is desirablethat at least a part of the sodium nitrate ingredient be dissolved inthe liquid. The addition of sodium nitrate makes it possible to increasethe total inorganic nitrate salt content of a saturated solution at agiven temperature. It also makes it possible, when sulfur is includedtoo, to sensitize the inorganic nitrates directly. Apparently, thepresence of sulfur makes it possible to convert the sodium nitrate tosodium sulfate. This releases more energy than does the reaction whichresults when sulfur is not present. In providing an easier route for thechemical breakdown of the sodium nitrate, the whole composition issensitized.

The ingredients named so far, generally speaking, should-be soproportioned as to give reasonable chemical balance between fuel andoxidizer material. In a simple case, using sulfur as the only fuel, withsodium nitrate as the oxidizer, the reaction between the sodium nitrateand the sulfur proceeds as follows:

2 (Mol. wt.) l+32- 142+28+32 This reaction proceeds more readily withsodium nitrate than with ammonium nitrate; hence the use of sodiumnitrate is desirable.

Since solubility of ammonium nitrate as well as that of sodium nitrate,and in fact of most salts, decreases as temperature is lowered, theincorporation-of the second inorganic nitrate salt into the compositionlowers the crystallization point or so-called fudge point of the liquidsolution for a given total salt concentration. However,

additional sodium nitrate beyond that which can be dis solved may be andpreferably is used. Sodium nitrate in this form not only adds to theoxidizer total content but also contributes to sensitivity of the slurryin conjunction with sulfur.

It is also desirable, according to the present invention, to add a smallamount of sulfur as a sensitizer. Sulfur also has fuel value and tendsto improve the oxygen balance in high inorganic nitrate compositions.Proportions preferred are between 1 and 6 percent by weight, preferably2 to 5%.

In order to produce an explosive slurry which will thicken on standingin the borehole and in order also to reduce water loss and to resistdilution of the composition by ground water which may be present in thehole,

a thickener is generally required. For this purpose a small amount ofguar gum, from 0.1 to 2% by weight is preferred. However, the guar gummay be replaced in part by other thickeners if desired. Starch has lessthickening capacity but is usually satisfactory for this purpose sinceit also has some fuel value, in addition to its thickening properties,in water solutions or slurries.

As noted above, only dry fuel materials may be added to the extentrequired for good oxygen balance and consistent with the slurryproperties desired. Materials such as gilsonite, or other heavy andpreferably solid carbon or hydrocarbon residues that can be comminuted,such as hard asphalt, bituminous coal, finely divided carbon, andcharcoal may be used. Dry starch, above the quantity that can be takenup by the liquid in the slurry, also is a desirable ingredient in somecases. The total of such dry fuels may vary from about 5 to 15% of theweight of the finished composition, preferably between about 7 and 12%.

An optional but usually highly desirable ingredient is aluminum powder.It is an effective sensitizer, as noted above. Moreover, it contributesconsiderable energy as a fuel. Proportions of to 3% or more ofaluminisien by weight, based on the total composition, may be u Otherfuels, or additional quantities of those mentioned above, may be addedto the extent that they do not interfere with the requisite fluidity ofthe slurry and provided they do not increase the density of thecomposition too much. The density of a slurry blasting composition,according to the present invention, should not exceed about 1.4 gramsper cc.

Example 1 A composition was prepared by dissolving 54 parts by weight ofammonium nitrate in 13% parts of water at 60 C. temperature. To thiswere added about 9 parts of sodium nitrate-about all that would go intosolution. A further quantity of 10 parts of dry granular sodium nitrate,which did not dissolve, was added thereafter, 19 parts in all.

To the resulting slurry which was still quite fluid, there were added 4parts by weight of flowers of sulfur, 4.5

parts of powdered gilsonite and 3 parts of starch. then one-half part byweight of a thickener, guar gum in this case, was added, making a totalof 98.5 parts by weight.

This material was found to have a critical diameter, d,,, forself-propagation of an explosion in an unconfined column six diameterslong, of about 6 inches at 35 C. This is satisfactory for many locationsbut not for all. Upon addition of 2 parts of finely powdered aluminum(paint grade) the sensitivity was further increased enough that thenmterial was self-propagating at 5' C. instead of 35' C.

Example 2 A composition similar to that of Example 1 'was preparedexcept that l parts of water and parts of ethylene glycol were usedinstead of 8% parts of water. Results were essentially the same as inExample 1, so far as sensitivity is concerned. The compositions of bothExamplea l and 2 were apparently very nearly equal in energy to slurriesof ammonium nitrate sensitized with TNT. They are appreciably lessexpensive.

In general, for a true slurry, the composition will contain enoughliquid to make it flow freely as a quasi-liquid, for most applications.This liquid may be all water, or it may contain water compatible liquidsof various types, such as alcohols, glycols and oxygen derivatives ofhydrocarbons in general. Aqueous solutions of fuel materials, e.g.molasses, may be included.

By balancing the excess oxidizer content ofthe ammonium nitrate withother fuel components, e.g. solid fuels such as gilsonite, starch,carbon black, and the like, proportions of sodium nitrate and sulfur maybe varied from S to 25% by weight of the former and about t to 8% of thelatter. For better operation, excess oxygen from the principal inorganicnitrate component may be balanced as fully as desired by use of otherfuel componenfs as described above.

Other modifications may be made within the spirit of the invention andwithin the limits outlined above. Additional fuel ingredients beyondthose named above, such as sugar, molasses and the like, may be addedExplosive sensitizers such as TNT, nitro starch, cellulose nitrate andnitro methane may be used,] along with the sodium nitrate and sulfur ifdesired. Aluminum may be added in proportions of about to to 1% byweight. Preferably, in these compositions smaller quantities of aluminumwill be used than conventionally, since aluminum is often a powerfulsensitizer as well as a fuel. Generally speaking, aluminum content,particularly of particles below 10 mesh (Tyler) in size will not exceed3%.

It will be understood that, in the claims that follow, it is intended tocover the various modifications mentioned above such other changes andvariations in composition and in procedure as would suggest themselvesto those skilled in the art, as far as the prior art properly permits.While slurries which are relatively liquid are usually preferred, itwill be understood that other moisture-containing compositions, whichmay not flow freely in the sense of a true liquid, but which areplasticized and capable of self conformation to a surrounding orsupporting structure or surface are also within the purview oftheinvention, at least in its broader aspects. The moisture need not bepure water but may comprise water and water-compatible liquids such asalcohols, glyool glycerol and the like. This liquid may comprise broadlyfrom 5 to 25% of the total, more generally 12 to 20%, with narrowerlimits for specific compositions.

What is claimed is:

l. A [moisture-containing] slurry explosive composition which is free ofnitrated organic explosive ingredients and which contains from about 5to 25 percent by weight of a [moistening] liquid, the major part ofwhich liquid is water, 40 to 70 percent of ammonium nitrate, [and] asensitizcr comprised of a combination of 2 to 25 percent of sodiumnitrate and l to 8 percent of elemental sulfur, based on the totalcomposition and'a fuel having a tendency to balance excess oxygen ofsaid ammonium nitrate and sodium nitrate.

2. A composition according to claim 1 [to] which [is added] contains 0.5to 3 parts of aluminum powder below about mesh particle size as anadditional fuel and sensitizer.

3. Composition according to claim 1 to which other fuels are added whichare non-explosive per se.

4. Composition according to claim 1 which contains 0.1 to 2 percent of aslurry thickener.

5. Composition according to claim 4 wherein the thickener is guar gum.

6. Composition according to claim 1 which contains 12 to 20 percent ofthe liquid.

1. Composition according to claim 6 which [also] contains a carbohydratefuel.

8. Composition according to claim 1 which [also] includes a carbohydratefuel.

9. A slurry explosive composition which is free of nitroted organicexplosive ingredients and which contains suflicient liquid to make itflow freely as a quasi-liquid, at least the major proportion of saidliquid being water, at least 50 percent by weight of ammonium nitrate, 2to 25 percent of sodium nitrate, a carbonaceous fuel and about one-fifthas much sulfur as sodium nitrate, by weight, whereby the sodium nitrateand the sulfur tend to sansitine the ammonium nitrate.

10. Composition according to claim 9 wherein at least a part of thesodium nitrate is not in solution.

11. Composition according to claim 10 wherein undissolved sodium nitrateand sulfur are intimately mixed to form an effective sensitiner.

12. Composition according to claim 10 which also contains not more than3 percent by weight of finely divided aluminum.

13. A slurry explosive blasting composition which is free ofself-explosive ingredientscomprising a saturated solution of aninorganic nitrate selected from the group which consists of ammoniumnitrate and ammonium nitrate mixed with a minor proportion of sodiumnitrste,

said inorpnic nitrate comprising at least half the total weight of thecomposition, a quantity of undissolved particulate sodium nitrate, aboutone-fifth as much sulfur as total sodium nitrate, not more than 10% ofparticulate metallic aluminum, and a thickening agent in suflicientproportions to reduce penetration of said slurry by ground water.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS

